Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-06-17
2004-05-04
Tran, Binh (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S275000, C060S280000, C060S295000, C060S311000
Reexamination Certificate
active
06729128
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2001-192331 filed on Jun. 26, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a technology for reducing or eliminating suspended particulates in exhaust gas produced from an internal combustion engine.
2. Description of the Related Art
The exhaust gas from internal combustion engines and, particularly, diesel engines, contains suspended particulates, such as black smoke (soot) and the like. It is strongly demanded that the total amount of carbon-containing suspended particulates emitted into the atmosphere be reduced in order to prevent further air pollution. A like demand exists regarding generally termed direct injection type gasoline engines in which gasoline is injected directly into a combustion chamber, because carbon-containing suspended particulates may be discharged together with exhaust gas depending on the engine operation conditions.
One proposed technology for reducing the carbon-containing suspended particulates emitted from an internal combustion engine and, particularly, a diesel engine, is a technology that removes suspended particulates from exhaust gas by using a heat-resistant filter loaded with an oxidation catalyst (Japanese Examined Patent Application Publication No. 7-106290). In this technology, suspended particulates in exhaust gas are collected by the filter, and the collected particulates are burned in exhaust gas at relatively low temperature (typically, 350° C. to 400° C.) due to the effect of the oxidation catalyst. Thus, by collecting and burning carbon-containing particulates in exhaust gas, the amount of suspended particulates released into the atmosphere can be considerably reduced.
However, in some cases, the temperature of exhaust gas becomes lower than the temperature (350° C. to 400° C.) that allows combustion of collected carbon-containing particulates. Therefore, during use of a filter, particulates deposit on the filter, thus giving rise to the problem of filter clogging. Specifically, under a condition that the exhaust gas temperature is lower than the temperature that allows combustion of collected carbon-containing particulates, suspended particulates in exhaust gas deposit on the filter. If the exhaust gas temperature sufficiently rises, combustion of carbon-containing particulates is resumed. However, some particulates on the filter may remain unburned if a great amount of particulates has deposited, and therefore needs a long time for complete combustion thereof. Furthermore, it is known that the carbon-containing particulates deposited on the filter gradually become less apt to burn. As incombustible particulates cover the oxidation catalyst, it becomes difficult to burn carbon-containing particulates on the filter. As the collected particulates cannot be appropriately processed, the filter becomes clogged in some cases.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a technology capable of effectively reducing carbon-containing particulates suspended in exhaust gas without allowing a filter to be clogged.
A first aspect of the invention is an emission control apparatus for reducing carbon-containing particulates contained in an exhaust gas from an internal combustion engine. The emission control apparatus includes a heat-resistant filter provided in a passage of the exhaust gas for collecting the carbon-containing particulates and controlling the exhaust gas through combustion of the particulates collected, a temperature increase need determining device that determines whether to increase a temperature of the heat-resistant filter, and a dynamic pressure increasing device that increases a dynamic pressure of the exhaust gas on the heat-resistant filter if it is determined that the temperature of the heat-resistant filter is to be increased.
The emission control method of the invention corresponding to the above-described emission control apparatus is an emission control method for reducing carbon-containing particulates contained in an exhaust gas from an internal combustion engine. The method includes the steps of: collecting and burning the carbon-containing particulates by using a heat-resistant filter provided in a passage of the exhaust gas; determining whether to increase a temperature of the heat-resistant filter; and increasing a dynamic pressure on the exhaust gas on the heat-resistant filter if it is determined that the temperature of the heat-resistant filter is to be increased.
The invention has been accomplished based on consideration of a phenomenon found by the inventors in which the temperature of a heat-resistant filter provided in an exhaust passage rises if the dynamic pressure of exhaust gas discharged from an internal combustion engine acts on the heat-resistant filter. As a preparation for description of the operation and advantages of the invention, this newly found phenomenon will be briefly described.
FIGS. 19A and 19B
are diagrams conceptually illustrating the phenomenon in which the dynamic pressure of exhaust gas acting on the heat-resistant filter increases the filter temperature.
FIG. 19A
conceptually illustrates a laboratory device in which a heat-resistant filter E is disposed in an exhaust pipe of an internal combustion engine A (representatively, a diesel engine). The internal combustion engine A draws in air from an intake pipe B, and burns fuel within a combustion chamber C, and discharges exhaust gas via an exhaust pipe D. Carbon-containing suspended particulates contained in exhaust gas, such as sooth and the like, are collected by the heat-resistant filter E provided in the exhaust pipe D. The temperature Tg of exhaust gas flowing into the heat-resistant filter E, and the temperature Tf of the heat-resistant filter can be measured.
Using the foregoing device, the temperature Tg of exhaust gas flowing into the heat-resistant filter and the filter temperature Tf were measured while the operation condition of the internal combustion engine A was changed. The filter temperature Tf was found to always exhibit a higher value than the inlet exhaust gas temperature Tg. Therefore, the inlet exhaust gas temperature Tg and the amount of increase of the filter temperature Tf from the inlet exhaust gas temperature Tg (dT=Tf−Tg) were determined while the exhaust gas temperature was changed with other factors, such as the amount of flow of exhaust gas and the like, being kept fixed as much as possible. Results are indicated in FIG.
19
B.
As indicated in
FIG. 19B
, the amount of increase dT of the filter temperature exhibits a tendency of substantially linearly increasing with increases in the inlet exhaust gas temperature Tg. Therefore, it is assumed that the phenomenon in which the filter temperature Tf becomes higher than the inlet exhaust gas temperature Tg is based on a mechanism described below.
That is, the heat-resistant filter E has a gas flow resistance. Therefore, when exhaust gas passes through the heat-resistant filter E at great flow speed, exhaust gas is impeded by the heat-resistant filter E, so that a portion of the speed of exhaust gas is converted into pressure. This pressure increase is expressed as dP. According to teaching in thermodynamics, three variables of pressure P, temperature T and specific volume v satisfy the following relationship:
P·v=R·T
(1)
where R is a gas constant. Therefore, if the pressure P increases by dP due to impediment of flow of exhaust gas by the heat-resistant filter E, the exhaust gas temperature also increases by dT so as to satisfy equation (1). That is, the phenomenon in which the filter temperature Tf is always higher than the inlet exhaust gas temperature Tg is considered to be based on the following mechanism. That is, exhaust gas is compressed in the heat-resistant filter due to the dynamic pressure, so that the gas temperature correspondingly rises and the exhaust gas with th
Kodama Yoshitada
Oyama Naohisa
Shiratani Kazuhiko
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